Method of monitoring a shutdown cycle of an air cycle machine of an aircraft

What is claimed is: 
     
       1. A method of monitoring an air cycle machine of an aircraft comprising:
 driving a rotary shaft of an air cycle machine; 
 disconnecting a driving source to allow the rotary shaft to slow the rotary shaft; 
 extrapolating a shutdown cycle data and estimating when a shutdown cycle time will breach a predetermined threshold; and 
 monitoring a shutdown cycle of the rotary shaft. 
 
     
     
       2. The method of  claim 1 , wherein the monitoring further includes monitoring time required for the rotary shaft to slow to a selected rotational velocity from an operational rotational velocity. 
     
     
       3. The method of  claim 1 , further comprising communicating monitored data to a controller and performing an action in response to shutdown cycle times breaching a selected threshold. 
     
     
       4. The method of  claim 1 , wherein monitoring takes place during a ramp down period of air cycle machine operation. 
     
     
       5. The method of  claim 1 , wherein the monitoring step lasts at least 30 seconds. 
     
     
       6. The method of  claim 5 , wherein the monitoring step includes a sampling rate of between 1 and 2 samples per second. 
     
     
       7. The method of  claim 1 , wherein at least one sensor operatively connected to the rotary shaft monitors the shutdown cycle of the rotary shaft. 
     
     
       8. The method of  claim 7 , further comprising monitoring at least two ramp down cycle times. 
     
     
       9. The method of  claim 7 , further comprising monitoring multiple shutdown cycles. 
     
     
       10. The method of  claim 9 , further comprising monitoring changes between shutdown cycles. 
     
     
       11. The method of  claim 7 , further comprising performing an action with respect to the air cycle machine prior to a shutdown cycle time reaching the predetermined threshold. 
     
     
       12. The method of  claim 11 , wherein the action includes sending an alert to a flight crew or maintenance crew of an aircraft on which the air cycle machine is included. 
     
     
       13. The method of  claim 11 , wherein the action includes removal of the air cycle machine from operation.